This invention relates to personal protection devices incorporating impact and load absorbing mechanism of a type that can be used in equipment for giving protection and comfort to a user and more particularly to systems used in protective gear such as helmets and body protectors.
As force is applied to the body of a human the body will begin to experience discomfort at some level of force. When used to counteract this level of force, load-absorbing devices are used to improve comfort. As the level of applied force increases, a force is reached beyond which damage to the body occurs. Impact-absorbing devices are used to absorb such forces and afford bodily protection.
The functional principals operative in this field include: (1) absorption of the energy of the applied force at the point of impact, (2) distribution of absorbed energy throughout a larger volume or area of impact cushioning material, (3) dissipation of the energy of the impact force through the structure of the cushioning material by kinetic thermal or chemical means, and (4) release of the absorbed and distributed energy at a slower rate and lower level of intensity to the surrounding structures including the underlying portions of the body.
Typical constructions of such devices for personal comfort and protection include an external layer and an internal layer. The external layer is useful to protect the internal layer from direct damage resulting from the external force. The external layer may be pliable and durable as in a chest protector or it may be rigid and durable as in a helmet construction. Typically the external layer does not absorb a large percentage of the impacting energy into its own structure but serves to distribute the energy of applied force over a larger surface area of the internal structure. The internal layer, often referred to as the cushioning layer, absorbs, distributes and dissipates the energy of the impact force.
In the past many materials have been used to provide the internal cushioning layer depending on whether or not the external area is rigid or non-rigid. Examples of protective equipment having a rigid external layer include helmets, shoulder pads and shin pads. Examples of protective equipment with non-rigid external layers would be chest protectors and hockey goalies leg pads.
Foam cushioning has been used for many years as an energy absorbing internal layer. It has been used as the sole component of this layer and has also been used in combination with other energy absorbing materials such as woven straps or air-filled chambers as found in U.S. Pat. No. 3,994,022 to Villari et al and U.S. Pat. No. 5,014,365 to Schultz. Major problems with foam type energy absorbing structures are that: (1) the energy is not easily distributed throughout the structure and therefore force of impact must be absorbed within the immediate locale of the impact, (2) the foam is relatively easily deformed to the extent that the maximum energy which can be absorbed is reached quickly with any further energy transferred directly from the rigid shell to the underlying anatomical structures, sometimes referred to as xe2x80x9cbottoming outxe2x80x9d, (3) the recovery profile, the time required for the energy absorbing structure to return to its original state following an impact, may be such that it is inefficient at absorbing repeated impacts, and (4) repeated impacts may cause fatigue and a break down of the energy absorbing structure of the foam thereby diminishing its efficiency.
Fluid filled chambers have been used as energy absorbing internal layers for protective helmets. Some designs are used in combination with foam cushions as shown in U.S. Pat. No. 4,375,108 to Gooding. Also certain other designs utilize multiple isolated chambers containing gas located separately within a rigid shell as disclosed in U.S. Pat. No. 4,586,200 to Poon. Additionally, there are designs of gas filled chambers, which are in communication with each other such that gas may flow from one chamber to the next. The flow of gas from one chamber to the next theoretically can be unrestricted but in practice, flow is restricted by the internal geometry and composition of the structure that connects the chambers and the resistance of the adjacent chamber to accept additional gas as well as any external pressure subsequently applied to the second chamber. This is exemplified by the previously mentioned patents to Schulz and Gooding. The flow of gas from a first chamber to a second chamber may be intentionally restricted by connecting structures incorporating valves or crimped mechanisms which serve to impede gas flow as seen in U.S. Pat. No. 4,566,137 to Gooding or U.S. Pat. No. 4,038,700 to Gyory.
In all prior art helmet structures, gas filled chambers are located within the structure of the rigid external layer. In essence these are all closed cell systems within the confines of a rigid shell. Such closed cell systems present certain problems. For example, the energy of the impact force must be absorbed and dissipated within the local or immediately contiguous area, as the energy is not distributed evenly throughout the helmet. Additionally, if the initial force is applied over a large area, or more than one force is applied at separate locations, the energy may not be able to be distributed at all from one region to a second region thus increasing the likelihood of transfer of energy to the underlying body which is to be protected. Also, in the unrestricted flow situation, all of the gases may be emptied from a chamber allowing further energy to be transferred to the underlying anatomical structures. In the case of chambers with restricted flow the energy is more likely to be transferred to the underlying anatomical structure. In any of these designs, the initial force may exceed the structural capabilities of the chamber causing it to rupture. Where any flow of gas between chambers is allowed, the recovery profile of any individual chamber is unclear, increasing the likelihood that more energy from repeated impacts will be transferred to the underlying structure.
As energy-absorbing characteristics of the foregoing helmet systems are exceeded, the energy is transferred to the underlying structures, such as the skull or brain. This transfer of energy is non-linear, defined by a more complex equation in which small increases in external force produce ever-larger increases in the energy transferred to the head. This is not unlike the changes that occur inside the skull following a closed head injury. Small increases in brain swelling are able to be tolerated with little change in intra-cranial pressure until the enclosing structure of the skull is filled or xe2x80x9cbottomed outxe2x80x9d. After that capacity is filled, small increases in brain volume produce ever-larger increases in intra-cranial pressure with dire consequences.
With respect to devices, which have a non-rigid external layer such as body protectors including chest guards, the external layer is usually durable and pliable. It is used to protect the internal cushioning layer from damage, by abrasion and cuts for example. It also may be intended to flex as the body of the user flexes. The internal layers of these devices have been constructed of foam material, fibers such as cotton, gas filled chambers and liquid filled chambers. Examples can be found in U.S. Pat. No. 3,999,220 to Keltner, U.S. Pat. No. 3,995,320 to Zafuto, U.S. Pat. No. 4,453,271 to Donzis, and U.S. Pat. No. 5,235,703 to Maynard. Gas filled chambers have the advantage of being lightweight and are able to conform easily to the anatomical shape of the user. Such structures as used in the prior art may employ gas filled chambers with either communicating chambers or non-communicating chambers and share the problems of energy transfer and unstable recovery profiles as discussed above.
It is an object of the invention to provide protective equipment incorporating load-absorbing mechanisms to improve the comfort of the user at levels of force below forces which might cause injury and to protect the body of the user from injury due to higher levels of force.
Another object of the invention is to provide protective equipment incorporating fluid filled load-absorbing elements in the area of the expected loads and in fluid communication with reservoir bladders located remotely from the impact areas to absorb and dissipate energy away from the impact area.
The objects of the invention are attained by a load or impact absorbing system incorporating a resilient, flexible bag containing fluid such as air under pressure which is placed in a position between the user and the probable load or path of impact. The bag communicates through a fluid conduit with a resilient reservoir of elastomeric material, having a collapsed condition at rest and which resists inflation until a predetermined pressure is exceeded within the load-absorbing bag. As this pressure is exceeded fluid is transferred from load absorbing bag via the conduit into the reservoir. As the external force is removed, the reservoir collapses to exhaust fluid and return it to the load-absorbing bag upon termination of the impact load. Single or multiple load absorbing systems may be employed in protective equipment such as helmets or chest protectors.